Final Thesis Defense Crop and Soil Science M.S. Degree
December 19, 2025 9:45AM - 10:45AM
Candidate’s Name: Blair Van Agen
Date: December 19th, 2025
Time: 9:45 am in PSSB A271
Impacts of Regenerative Agriculture on Yield Stability and Water and Nitrogen Use Efficiency
Members of the Examining Committee and their Department:
1. Dr. Bruno Basso – Earth and Environmental Sciences; Plant, Soil and Microbial Sciences;
W.K. Kellogg Biological Station
2. Dr. Karen Renner - Plant, Soil and Microbial Sciences
3. Dr. Christine Sprunger – Plant, Soil and Microbial Sciences; W.K. Kellogg Biological Station
The seminar precedes the examination, at the time above
ABSTRACT
Regenerative agriculture (RA) practices such as cover cropping and no-till are increasingly promoted to improve soil health, resource use efficiency, and climate resilience. However, their long-term effects on crop yield, yield stability, and underlying soil nitrogen and water dynamics remain uncertain, especially with spatial variability among agricultural fields. This thesis evaluates how RA influences crop productivity, spatial yield patterns, and resource-use efficiency across yield stability zones (YSZs) in commercial maize and soybean fields in Michigan.
Chapter 1 assesses how RA adoption affects sub-field spatial variability using long-term yield monitor data from ten farm fields in Springport, MI. Yield stability zones (high, medium, low, and unstable) were quantified for 6–9 years before and 9–10 years after RA implementation. Although RA did not significantly change average maize (+9%) or soybean (–3%) yields, it substantially improved whole-field yield stability, decreasing the coefficient of variation from 27% to 17%.
RA also increased the proportion of high-yielding zones by 28%, largely through conversion of 21% of previously unstable areas into more stable, productive zones. These results indicate that RA enhances long-term spatial yield resilience even when mean yields remain unchanged.
Chapter 2 investigates soil nitrogen availability, soil water balance, biomass accumulation, crop yield, water use efficiency (WUE), and nitrogen use efficiency (NUE) under RA versus conventional agriculture (CA; tillage and bare fallow) across YSZs over two growing seasons. Soil inorganic N did not differ by treatment or YSZ. Yield responses to regenerative agriculture practices varied by crop and year: in the single maize year, CA produced higher yields, while soybean showed mixed responses across two years—CA yielded higher in one year, whereas RA yielded higher in the other.
Although maize yielded higher under CA management due to higher nitrogen uptake, RA achieved greater NUE, particularly in low- and medium-stability zones. Neither soil water balance nor WUE differed significantly between treatments.
Overall, the responses of soil water and N to RA were limited; however, these results are based on only one maize season and two soybean seasons. This limited timeframe might not be sufficient to capture RA practices effects. Multi-years observations might be required to account for weather variability and management interactions. Despite this limitation, RA management improved long-term yield stability and converted unstable areas into consistently productive zones, highlighting its potential to enhance resilience in upper Midwest cropping systems.
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